The present invention generally relates to the technical field of wireless communication, and more particularly, to a control device for regulating the circuit constant of an antenna matching circuit.
It is necessary for radio communication equipment to implement impedance matching between the antenna and the internal circuit; otherwise, the signal energy cannot be effectively radiated from the antenna or supplied to the internal circuit.
In mobile communication, the input/output impedance of the antenna varies depending on the environment in actual use. For instance, in receiving a radio wave, the input impedance of the antenna of radio communication equipment placed on a desk differs from the input impedance of that radio communication equipment held in hand. For this reason, radio communication equipment is furnished with an a antenna matching circuit for adjusting the input impedance of the antenna so as to equal or approximate the characteristic impedances of the internal circuit and the transmission line. Such a matching circuit is structured with high-frequency variable elements (such as capacitors and coils capable of changing the impedance). By adjusting the impedances of the high-frequency variable elements, impedance matching is achieved between the antenna and the internal circuit.
Conventional matching circuits are disclosed in, for example, JPA 11-251928, JPA 8-195638, and JPA 8-148960. The matching circuit disclosed in JPA 8-148960 adjusts the impedance between only two levels, and therefore, it is difficult for this matching circuit to flexibly adjust the antenna impedance according to the status of use. The circuits disclosed in JPA 11-251928 and JPA 8-195638 are capable of adjusting the impedance of a high-frequency variable element over a broader range than that of the circuit disclosed in JPA 8-148960. However, these circuits require a dedicated digital processor for adjusting the impedance of the high-frequency variable element. To provide a dedicated digital processor, various elements, such as an analog-to-digital converter, a CPU, a digital-to-analog converter, and other necessary devices, have to be assembled and a complicated control algorithm has to be executed.
To adjust the impedances of multiple variable elements, a digital processor has to be provided for each of the variable elements. Accordingly, the techniques disclosed in JPA 11-251928 and JPA 8-195638 are unsuitable for applications for regulating multiple elements.
In addition, with the technique disclosed in JPA 11-251928, a detected signal is used as a parameter representing impedance mismatch of the antenna, which is then used as a control signal for adjusting the impedance of the high-frequency variable element. Accordingly, if the detected signal has only a small quantity of power, the response speed for controlling the high-frequency variable element becomes slow.
The above-described drawbacks in the known techniques become conspicuous when applied to mobile communications involving cellular terminals traveling at high speed or data transmission for transmitting a large quantity of data at a high rate. Such high-speed mobile communications and high-speed data transmission are important technologies, attracting more and more attention. It is difficult for the conventional matching circuits to deal with these demands.